linux-kernel - [PATCH 27/33] x86/fpu: Simplify fpu__activate_fpstate

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Date:   Sat, 23 Sep 2017 15:00:10 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH 27/33] x86/fpu: Simplify fpu__activate_fpstate_read()

fpu__activate_fpstate_read() can only ever be called for a non-current,
non-executing (stopped) task - so make sure this is checked via a warning
and remove the current-task logic.

This also fixes an incorrect (but harmless) warning introduced by one of
the earlier patches.

Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Eric Biggers <ebiggers3@...il.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/core.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 93103a909c47..7bd4edb76c1d 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -256,26 +256,18 @@ EXPORT_SYMBOL_GPL(fpu__activate_curr);
  *
  * If the task has not used the FPU before then initialize its
  * fpstate.
- *
- * If the task has used the FPU before then save it.
  */
 void fpu__activate_fpstate_read(struct fpu *fpu)
 {
-	/*
-	 * If fpregs are active (in the current CPU), then
-	 * copy them to the fpstate:
-	 */
-	if (fpu->fpstate_active) {
-		fpu__save(fpu);
-	} else {
-		if (!fpu->fpstate_active) {
-			fpstate_init(&fpu->state);
-			trace_x86_fpu_init_state(fpu);
+	WARN_ON_FPU(fpu == &current->thread.fpu);
 
-			trace_x86_fpu_activate_state(fpu);
-			/* Safe to do for current and for stopped child tasks: */
-			fpu->fpstate_active = 1;
-		}
+	if (!fpu->fpstate_active) {
+		fpstate_init(&fpu->state);
+		trace_x86_fpu_init_state(fpu);
+
+		trace_x86_fpu_activate_state(fpu);
+		/* Safe to do for current and for stopped child tasks: */
+		fpu->fpstate_active = 1;
 	}
 }
 
-- 
2.11.0